1. Field Of The Invention
The advent of hybrid DNA technology provided a unique opportunity to produce peptides of any sequence of naturally-occurring amino acids. Thus, for the first time, macromolecules could be prepared at will from a large number of different monomers to provide a specifically defined sequence. Once the feasibility had been established, there was then an interest in the economics of the technology, in providing systems which could be adapted to the production of particular products.
In part, because of the familiarity with E. coli, E. coli was an obvious host for research expression and potentially for commercial expression of products of interest. However, E. coli, as well as other prokaryotes, have a number of disadvantages. Many of the prokaryotes produce endo- or exotoxins. Therefore, the resulting product must be carefully purified to ensure the absence of any materials which would affect the health of the patient. This can be particularly troublesome, where the product is administered chronically.
Yeast as a host does not suffer from many of the disadvantages of prokaryotes and, furthermore, has a number of advantages. Yeast has been used for a long time in fermentation, so that there are a number of commercial hosts which have a number of desirable properties, such as resistance to viral infection, rapid growth, stability, and the like. In addition, yeast can provide in certain situations glycosylation of the product, so as to provide a peptide product which has a verisimilitude to the naturally-occurring glycosylated product.
In order to use yeast as a host, it will be necessary to provide a number of different constructs which allow for expression under a variety of conditions. In many situations, one may wish to have controlled expression, where a change in the nutrient medium may actuate or inhibit expression. Furthermore, since yeast secretes a number of different products naturally, the secretion mechanism may be available for secretion of a variety of peptides foreign to yeast. Thus, yeast provide an attractive opportunity for the development of economical and efficient production of peptides.
2. Description Of The Prior Art
Krebs, J. Biol Chem. (1953) 200:471 and Maitra and Lobo, ibid. (1971) 246:475 describe properties of glyceraldehyde-3-phosphate dehydrogenate (GAPDH) in yeast. Cloning of GAPDH genes or the pyruvate kinase (PyK) gene has been described by Holland, et al., Basic Life Science (1981) 19:291; and Kawasaki and Fraenkel, Biochem. Biophys. Res. Comm. (1982) 108:1107. Yeast promoters which have been linked to foreign genes include alcohol dehydrogenase I (ADHI) (Valenzuela, et al., Nature (1982) 298:347; Hitzeman, et al., ibid. (1981) 293:717) and phosphoglycerate kinase (Tuite, et al., EMBO (1980) 1:603; Hitzeman, et al., Science (1983) 219:620). Beier and Young, Nature (1982) 300:724 reports the use of ADR3 as a regulatory sequence.